Referring to FIG. 1, a schematic cross-sectional view of an optical reading head of a conventional scanning apparatus 1 is illustrated. The optical reading head 10 comprises a light source 101, plural reflective mirrors 102, a lens 103 and an image sensing module 104 are provided. During operation, the light emitted from the light source 101 is projected onto a document 11 to be scanned. The light reflected from the scanned document 11 is successively reflected by the plural reflective mirrors 102, and then focused by the lens 103. The focused light is then imaged onto an image sensor (not shown) of the image sensing module 104 to convert the optical signals into analog electrical signals. The light source 101, the reflective mirrors 102, the lens 103 and the image sensing module 104 are included within a casing 100. The casing 100 of the optical reading head 10 is driven by a driving device (not shown) so as to scan the whole document 11.
Please refer to FIG. 1 again. After the light source 101, the mirrors 102, the lens 103 and the image sensing module 104 are mounted within the casing 100 of the optical reading head 10, focusing and magnification correcting operations should be performed. At first, by properly adjusting the position of the lens 103, the optical signals would be clearly imaged onto the image sensor. Afterward, by simultaneously moving the lens 103 and the image sensing module 104, the tolerance of magnification for the optical reading head 10 would be equal to or less than an acceptable preset value. Generally, during the process of performing the focusing and magnification correcting operations, the lens 103 and the image sensing module 104 are firstly arranged on a base, and then the base is mounted on the casing 100. Under this circumstance, the assembler may correct the magnifying power of the optical reading head 10 by moving the lens 103 on the base to image the optical signals onto the image sensor. Then, by adjusting the location of the base, the lens 103 and the image sensing module 104 are simultaneously moved, thereby performing the magnification correcting operation.
An example of the above optical reading head is described for example in Taiwanese Patent No. 417931, entitled “Optical path adjustable mechanism of an optical system”. In such an optical path adjustable mechanism, a lens and an image sensing module are mounted on a base. The assembler may correct the magnifying power of the optical reading head by moving the lens on the base so as to image the optical signals onto the image sensor. Alternatively, by adjusting the location of the base, the lens and the image sensing module are simultaneously moved, and thus the magnifying power of the optical reading head is also corrected.
As previously described, the lens is moved on the base to perform the focusing operation of the image sensor and then the base is moved to perform the magnification correcting operation. This optical path adjustable mechanism, however, has some drawbacks. For example, since the lens is indirectly moved on the casing via the base to perform the focusing and magnification correcting operations, the accumulated tolerance of the optical reading head is increased, and thus the scanning performance is reduced.
On the other hand, it is important to stably move the base on the casing during the process of performing the magnification correcting operation. In accordance with the optical reading head described in Taiwanese Patent No. 417931, a resilient clip element is disposed on a side of the base such that the opposite side of the base is in close contact with the gliding pedestal. Under this circumstance, the base is advanced in close to bilateral sides of the gliding pedestal. Unfortunately, since the pushing force applied by the resilient element sheet is perpendicular to the advancing direction, the base is readily sloped rightwards or leftwards and fails to be stably moved along the gliding pedestal.
Moreover, after the focusing and magnification correcting operations are completed, the lens is glued onto the base so as to fix the position of the lens. Once the optical reading head needs be maintained and reworked and the lens needs to be replaced, the combination of the lens and the base would be replaced by a new one. Therefore, there is a need for developing an improved base capable of fixing a lens thereon and is easily detachable when the optical reading head is maintained and reworked and the lens needs to be replaced.